Background : This study was carried out to evaluation the effect of human platelet rich plasma (hPRP) on the bone repair process in rabbit model which could be used in many procedures of orthopedic or maxillofacial bone and implant reconstructive surgery.Materials and Methods : This study is a prospective experimental study on animal model. A critical size defect (10 mm) was created in the radial diaphysis of 24 rabbit and then supplied with human PRP (treatment group) or the defect left empty (control group). Radiographs of each forelimb was taken postoperatively on 1st day and at the 2nd, 4th, 6th and 8th weeks post injury to evaluate bone formation, :::union::: and remodeling of the defect. The operated radii were removed on 56th postoperative day and were evaluated for biomechanical properties and histopathological criteria.Results : The results indicate that human PRP (as a xenogenic PRP) in treatment group significantly promote bone regeneration in critical size defects compared with control group (p<0.05).Conclusion : This study showed that hPRP has a high regenerative capacity in critical size bone defects in rabbit model after 8 weeks.